Tiny bubbles could lead to big advances in holography

A little mermaid, made out of little bubbles(Credit: Kota Kumagai, Utsunomiya University)

If there's one thing that sci-fi movies and TV shows love, it's the idea of holographic displays that people can walk around and view from different angles, without any special headgear. Well, researchers from Japan's Utsunomiya University have come a step closer to making such technology a practical reality. They've created a system in which lasers are used to create tiny bubbles, which in turn make up three-dimensional images within a column of clear liquid.

Led by Yoshio Hayasaki, the team uses lasers that shoot femtosecond (one quadrillionth of a second) pulses of light into precise locations within a viscous liquid. As the liquid absorbs multiple photons at the points where those pulses are focused, small bubbles form. Because the liquid is fairly thick, those bubbles stay in place instead of floating to the top right away. Each one of them constitutes a three-dimensional pixel – or voxel – of the complete holographic image.

In order for that image to be seen easily, the liquid has to be exposed to an external light source such as an LED. The bubbles catch and scatter that light, causing the image to visually "pop out" from the surrounding liquid. It's what's known as a volumetric display, in that the display medium itself (as opposed to just the image) is three-dimensional.

The color of the image is determined simply by the color of the light. While this currently makes for images that are a single color at any one time, the scientists believe that in the future, projectors could be used to focus different colors onto different parts of the image simultaneously. Additionally, utilizing a system in which a current within the liquid burst the bubbles after they were formed and seen, it could be possible to have an animated or quickly-changing display.

So far, the team has created millimeter-scale 2D and 3D images. Once some of the technical hurdles are overcome, however, it is hoped that the technology could be used in museum displays, military terrain studies, or perhaps by doctors studying patients' anatomy. Down the road, it could even take the form of a consumer product.

"The volumetric bubble display is most suited for public facilities such as a museum or an aquarium because, currently, the system setup is big and expensive," says Kota Kumagai, first author of a paper on the study. "However, in the future, we hope to improve the size and cost of the laser source and optical devices to create a smaller system that might be affordable for personal use."